The present invention relates to a coated cutting tool insert with a sharp cutting edge particularly useful for machining of non ferrous materials such as titanium, aluminium, brass, bronze, heat resistant and super alloys, plastics as well as small part machining in steel and stainless steel.
For the machining of metals, like milling, turning and drilling, cutting tool inserts of cemented carbide having a rake face and clearance faces intersecting to form a cutting edge are used. The cutting edge should be sharp to provide low cutting forces and low energy consumption. However, cemented carbide is a brittle material and for that reason a sharp cutting edge is generally not strong enough. If it breaks, the cutting forces increase and the surface finish of the machined material will be poor. In order to strengthen the edge, it can be rounded to a radius of generally 10-50 μm, or provided with a chamfer or a land. The exact design of the edge depends on the material to be machined and is a compromise between acceptable cutting forces and strength of the edge. Some workpiece materials such as aluminium, etc., require a very sharp edge with minimal edge rounding. An excessively rounded edge can in such materials represent a worn edge and can affect the subsequent wear development. For the machining of such materials, uncoated cemented carbide inserts are generally used. If a coating is applied, the edge will be less sharp particularly if coated with CVD- or MTCVD-techniques. In addition, coated cutting edges require a certain amount of rounding to ensure a satisfactory application of a coating. It is however, a desire to be able to use coated inserts also for the machining of materials requiring sharp cutting edges.
US patent application 2006/0019120 A1 discloses a cutting tool insert for metal machining comprising a coating comprising at least one wear resistant layer and a substrate and said insert further comprising clearance faces and rake faces intersecting to form cutting edges. The cutting edge has essentially no edge radius. The coating has been removed by grinding on the clearance face at least close to the cutting edge. It has, however, been found that such an insert has in some applications insufficient wear resistance.